[v2] Migrate and improve unit test coverage of some files

.changeset/fast-yaks-kneel.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+`onSubmit` now has access to `createErrorMap`

packages/form-core/src/FieldApi/fieldTree.lib.ts

@@ -450,7 +450,7 @@ export function killField(
   reattachFormGroups()
 }
 
-export function canPruneField(field: AnyInternalFieldApi): boolean {
+function canPruneField(field: AnyInternalFieldApi): boolean {
   if (field._isKilled) return false
 
   if (field._refCount > 0) return false

packages/form-core/src/FormApi/FormApi.public.ts

@@ -9,6 +9,7 @@ import type {
   ParsedStandardSchemaIssues,
   ToFormErrorTypes,
   ToFormOutputs,
+  ValidationErrorMap,
 } from '../validation.public'
 import type { StandardSchemaV1Issue } from '../standardSchema.public'
 import type { FormListeners } from '../listeners.public'
@@ -62,6 +63,11 @@ export type CreateValidationErrorFn<in out TFormData> = <
   error: TError,
 ) => OnSubmitError<TError>
 
+export type CreateSubmitErrorMapFn<in out TFormData> = (
+  initial?: Partial<ValidationErrorMap<TFormData>>,
+) => ValidationErrorMap<TFormData> &
+  OnSubmitError<ValidationErrorMap<TFormData>>
+
 /**
  * Converts Standard Schema issues into an `onSubmit` validation error.
  *
@@ -146,6 +152,7 @@ export interface FormSubmitContext<
    * ```
    */
   createValidationError: CreateValidationErrorFn<TFormData>
+  createErrorMap: CreateSubmitErrorMapFn<TFormData>
   /**
    * Parses Standard Schema issues into an error returnable from `onSubmit`.
    *

packages/form-core/src/FormApi/handleSubmit.lib.ts

@@ -5,13 +5,16 @@ import {
   parseValidationResult,
 } from '../validation'
 import { parseStandardSchemaIssues } from '../standardSchema.lib'
+import { createErrorMap } from '../validation.public'
 import type { InternalFormApi } from './FormApi.lib'
 import type {
   FormValidateResult,
   FormValidationError,
   ValidationErrorInput,
+  ValidationErrorMap,
 } from '../validation.public'
 import type {
+  CreateSubmitErrorMapFn,
   CreateValidationErrorFn,
   OnSubmitError,
   ParseSubmitIssuesFn,
@@ -39,6 +42,14 @@ function createSubmitError<TError extends FormValidationError<any>>(
   return { [SUBMIT_ERROR]: error }
 }
 
+function createSubmitErrorMap<TFormData>(
+  initial?: Partial<ValidationErrorMap<TFormData>>,
+): ReturnType<CreateSubmitErrorMapFn<TFormData>> {
+  const map = createErrorMap(initial)
+  Object.defineProperty(map, SUBMIT_ERROR, { value: map })
+  return map as ReturnType<CreateSubmitErrorMapFn<TFormData>>
+}
+
 function createParseIssues<TFormData>(
   value: TFormData,
 ): ParseSubmitIssuesFn<TFormData> {
@@ -168,6 +179,7 @@ export async function runSubmissionProcess<TFormData>(
       validatorOutputs,
       value,
       createValidationError,
+      createErrorMap: createSubmitErrorMap,
       parseIssues: createParseIssues(value),
     })